Emergent Devonian Period: 419 - 359 mya
Features of the Devonian period: 419-359 mya:
4) Known as "The Age of Fishes", fishes with jaws appear, such as armored placoderms (the first fish with jaws, gills, and paired fins), now extinct, as well as the bony fishes (osteichthyes), i.e., both the ray-finned fishes, and the lobed-finned fishes, the latter foreshadowing the tetrapods.
5) Cartilaginous sharks (chondrichthyes) appear, the descendants of placoderms, but without the bony armor.
6) Tiktaalik, the transition form between fishes and tetrapods (vertebrates with 4 limbs) evolves, with the scales and fins of a fish, but a movable neck and rib-enclosed lungs of a terrestrial organism: the first air-breathing animals!
7) The Late Devonian gives rise to wingless insects, and salamander-like amphibians (labyrinthodonts).
8) The first forests and gymnosperms (seed plants, with the seeds in cones) arise.
1) has 7 geologically defined (GSSPs) stages.
2) High sea-levels defined most of the period, with southern glaciations just before its end, as well as Appalachian Mountain glaciers in North America (The Geologic Time Scale, 2012, p. 559).
3) This period is marked by the greatest carbonate production, with a peak of reef growth, the greatest diversity of marine fauna in the Paleozoic, the establishment of vascular plants, and the appearance and diversification of tetrapods (ibid., p. 559).